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| Siemens AG | 13 Jul 2011 |
Power at the bottom of the Sea
The depletion of onshore reserves is forcing oil and gas companies to exploit fields in the remotest places at increasing water depths. However, these subsea environments lead to a recovery gap compared to traditional surface wells. The Siemens subsea power grid will help close this gap by enabling subsea processing technologies such as pumping and compression to be more widely adopted.
Most experts agree that the days of easy oil recovery are over – a view that is evident from oil companies’ activities in increasingly remote offshore fields in ever-deeper waters.
But operating in deep water is fraught with challenges. The heavier oil, smaller fields, and tremendous water pressure in subsea environments means the oil is harder to extract, leading to a recovery gap compared to traditional surface wells that can be as high as 30 per cent.
Another important technical challenge is power distribution to these remote facilities. Indeed, full subsea processing is unthinkable without an industrial, heavy duty, highly reliable power systems directly on the seabed.
In response to the power needs of the oil and gas industry, Siemens is developing fully marinized subsea power systems that will make full subsea processing a reality. This can help oil and gas operators improve the recovery of wells from around 35 per cent to 65 per cent.
By delivering 36 kV over large dispersed fields in a depth of 3000 m, for the first time ever, Siemens power systems allow the cost-efficient operation of large subsea production facilities with multiple power consumers such as electrical driven pumps and compressors.
Experience in the field
With experience that stretches from wellhead-to-wire, Siemens is ideally placed to develop the solutions needed in the oil and gas industry.
Siemens operates across the whole energy value chain, with experience in sectors ranging from compression and pumping, through to power generation and distribution, automation and control, industrial IT, to lifecycle services.
Subsea compression is an area in which Siemens has been making advances – its STC-ECO motor compressor represents a quantum leap in subsea compressor technology. It will operate continuously on the seabed allowing economic and environmentally friendly recovery of oil and gas at even the most extreme depths. The design eliminates the need for seals between motor and compressor housings. The entire machine is contained within a hermetically sealed pressure casing. Despite its space-age technology, the compressor uses an essentially simple, highly robust modular construction, enabling it to operate with total reliability, continuously, 24-7, 365 days a year, for a minimum of five years without maintenance of any kind.
For more than 20 months, STC-ECO has operated with dirty process gas in modulating mode and under routine asset control. Inspection showed that all internal components were in perfectly good condition. This compressor is also suitable for subsea applications. In August last year, the compressor completed factory acceptance tests – a major milestone in the system qualification programme and for marinization of the equipment.
Building on success
The decision to move ahead with the subsea power was prompted about a year and a half ago to build on Siemens’ success in providing onshore or ‘topside’ equipment such as VSDs, transformers and switchgears.
Siemens has already had some experience of adapting its transformers for subsea operation. In 1998, the company delivered a subsea transformer for the Brazilian Petrobras PROCAP project at a depth of 1000 m. Around 65% of the potential oil discoveries will be in deep and ultra deep water. The development of a power transmission system in medium voltage and variable frequency for a long distance was necessary to reduce the number of platforms to drain giant fields.
Now the idea is to further tailor Siemens topside equipment for operation on the seabed at depths of 3000 m (10 000 ft) and step-outs of 200 km from the shore. Siemens will also be looking at the engineering related to infrastructure technology including connectors, penetrators and cables as part of the overall development.
Adapting to subsea environments
The necessity for going subsea is clear. Indeed, there is little choice in situations where no topside is available i.e. there is no platform, or there is no room on the platform for electrical equipment to support a new field tie in. Further, to improve the oil recovery, it is necessary to have subsea power distribution together with pumps on the seabed.
However, there are a number of challenges to operating on the seafloor. Components have to withstand an ultra-high external pressure: almost 300 bar (5000 psi) ocean depths of 3000 m (10000 ft). Additionally, components have to withstand sustained temperatures of around 4ºC and salt water immersion. Technology has to work remotely and be maintenance-free for long periods of time with remote monitoring to avoid costly outages.
Development path
Development of components for subsea power systems is following a carefully planned path. After completing numerous studies, Siemens took the decision to develop robust and fully marinized subsea power in 2010.
Siemens just officially opened a new test and fabrication facilities in Trondheim, Norway. This is a brand new 8000 m2 technology centre. The company is globalizing these efforts through additional setups in Houston, Rio de Janeiro and Singapore.
Today there are roughly 70 people working on the development projects. These projects are expected to be qualified around the 2013 timeframe. The exact timing will depend on how long the oil companies want for testing in shallow water etc.
In order to develop a successful solution it is important to have knowledge of how to design, construct, submerge and retrieve subsea structures. If a VSD has to sit on the seabed for 3-5 years, connections and penetrators etc. have to be designed in such a way to ensure that the units can be lifted when needed. The transformers and switchgear within the system also have to be designed so that they can be lifted separately.
When Siemens began developing its subsea power concept, one of the first tasks identified was the need to expand its expertise in engineering and marinization in order to fill any potential technology gaps.
In March 2011 Siemens acquired the two subsea specialists Poseidon Group AS and Bennex Group AS from Subsea Technology Group AS, Norway. Poseidon is a world leader in subsea marinization, engineering and consulting, while Bennex develops and manufactures subsea equipment mainly for subsea distribution, both electrical and hydraulic.
With the subsea processing market growing fast, the development of a subsea power grid will be essential in order to allow it to reach its full potential for Allowing Operators to deploy technology that improves their ability to recover hydrocarbons efficiently and effectively. As a solutions provider with experience right across the value chain, Siemens is well placed to lead the exploration to bring power to the bottom of the sea.
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